One of the many applications of Monte Carlo methods can be found in the field of medicine and cancer treatment. In 1997, researchers at the Lawrence Livermore National Laboratory (Operated by the University of California for the U.S. Department of Energy) created a hardware and software system called PEREGRINE (named after the patron saint of cancer patients, St. Peregrine), which can be used to analyze and propose radiation treatments for cancer patients. More than 100,000 patients die in the U.S. each year while receiving radiation treatments. PEREGRINE can save lives by improving the accuracy and effectiveness of these radiation treatments.

During any patient’s radiation treatments, he or she is exposed to many trillions of photons. It is in the patient’s best interest for this radiation to be concentrated on the tumor, and for no radiation to have an effect on any healthy tissue. Knowing where to aim the radiation and what levels of radiation to use is not an easy problem, and thus PEREGRINE was developed to model it.

How does PEREGRINE work? First, the patient goes through a series of CT scans, which are used to develop a computer model of his or her body. Then, using the Monte Carlo method, many millions of photons with randomly generated positions and intensities are sent through the computer model. The model is extremely complex: As one Lawrence Livermore Laboratory site says, “colliding with an electron in the skin, ionizing a hydrogen atom in the blood, perhaps being absorbed by calcium in the bone- [all of these are] calculated in the model.” The model shows how much radiation ends up focused on each portion of the affected area of the body. Using results from this simulation, doctors can find the optimal doses of radiation to give to the patient. Here is an example of part of what a doctor might see as output from the simulation (this image is of a patent’s lungs):

Studies have shown that applying Monte Carlo methods to cancer treatment like PEREGRINE does can improve radiation dosage estimates by up to 30% over other techniques. Part of the reason that PEREGRINE’s model is effective is that it takes into account the body’s different tissues (seen in the CT scans) rather than modeling it as one medium. In past years, Monte Carlo methods like PEREGRINE’s were infeasible because they are computationally expensive (in 1995 they could take over 200 hours, whereas now they can be done in under a minute). PEREGRINE is another example of the power of Monte Carlo methods in real world applications.

References:

http://en.wikipedia.org/wiki/Monte_Carlo_method

http://www.canberra.edu.au/irps/Archives/vol14no4/news.html

https://www.llnl.gov/str/Patterson.html